Fiberglass insulation products generally include matted glass fibers that are held together by a cured thermoset polymeric resole resin. During production of such products, streams of molten glass are drawn into fibers of varying lengths and then blown into a forming chamber where they are deposited with little organization, or in varying patterns, as a mat onto a traveling conveyor. The fibers, while in transit in the forming chamber and while still hot from the drawing operation, are sprayed with an aqueous resin binder solution. The residual heat from the glass fibers and the flow of air through the fibrous mat during the forming operation will generally evaporate most of the water from the resin binder, thereby leaving the remaining components of the binder on the fibers as a viscous or semi-viscous high-solids liquid. The resulting coated fibrous mat is generally referred to as a “wet blanket.” The coated fibrous mat or wet blanket, which is formed in a compressed state due to the high-velocity flow of air through the mat in the forming chamber, is then transferred out of the forming chamber to a transfer zone where the mat vertically expands due to the resiliency of the glass fibers. This vertical expansion can be important in the manufacture process of commercially acceptable fiberglass thermal or acoustical insulation products. Subsequently, the coated mat is transferred to a curing oven where heated air is blown through the mat to cure the binder and rigidly attach the glass fibers together.
Resole resin is a phenol-aldehyde resin having a molar ratio of phenol to aldehyde of about 1:1.1 to about 1:5. Preferably the phenol to aldehyde ratio is from about 1:2 to about 1:3. The phenol component of the resole resin can include a variety of substituted and unsubstituted phenolic compounds. The aldehyde component of the resole resin is preferably formaldehyde, but can include so-called masked aldehydes or aldehyde equivalents such as acetals or hemiacetals. Specific examples of suitable aldehydes include: formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, furfuraldehyde, and benzaldehyde.
Phenol-formaldehyde (PF) resole resins, as well as phenol-formaldehyde resole resins extended with urea (PFU resins), are used in conventional processes, and have been relied on heavily over the past several years to prepare binders for fiberglass insulation products. Though these resins are inexpensive and provide the cured fiberglass insulation product with the desired physical properties, they may often have high free formaldehyde content, and a distinctive or unpleasant odor limiting their use in certain applications. Further, during the manufacture of fiberglass insulation, the potential for formaldehyde emissions and worker exposure is present. Therefore, manufacturing facilities using PF and PFU resole resins as the main binder component for insulation products are often required to install expensive controls in order to minimize the possible exposure of workers to formaldehyde emissions and to install expensive abatement equipment for the process exhaust gases to meet certain Maximum Achieveable Control Technology (MACT) requirement standards. Options for formaldehyde-free products or processes include i) adding a formaldehyde scavenger to the binder to reduce or remove free formaldehyde and thereby limit its subsequent emission and/or odor; ii) allowing the resin reaction to proceed for longer periods of time to reduce the free formaldehyde present in the resin product; or iii) utilizing formaldehyde-free resin formulations.
The use of formaldehyde scavengers may lead to precipitation, resulting from the scavenger itself and/or the adduct between the scavenger and any residual formaldehyde being insoluble. Further, allowing the resin reaction to proceed for an extended period of time sufficient to afford target formaldehyde levels results in a resin product having a concomitantly higher molecular weight. Such higher molecular weight resins may lack the desirable properties for some applications, as many tend to be sticky, causing the binder and the binder-coated fiberglass product to adhere to production equipment. Furthermore, higher molecular weight PF resole resins tend to have a higher “tetradimer” content. Tetradimer is a highly crystalline PF dimer present in phenolic resins produced under base-catalyzed conditions, which often precipitates readily. Precipitation is even more likely when free formaldehyde in the resin is scavenged. Tetradimer precipitation can result in plugged spray nozzles, and in precipitate formation in resin binder storage tanks and in the resin itself, necessitating removal.
Accordingly, as an alternative to PF and PFU resole resins, formaldehyde-free resin formulations have received increased attention for use as binders in making fiberglass insulation and other products.